1. Field of the Invention
The present invention generally relates to planarizing systems and more particularly to an improved chemical mechanical polishing system with real-time polishing rate measurement and control.
2. Description of the Related Art
Chemical mechanical polishing/planarization (CMP) is becoming more popular as a choice for planarizing materials in today""s advanced integrated circuit devices. More specifically, the increased use of shallow trench isolation (STI) regions makes chemical mechanical polishing a more commonly used process.
Basically, in a chemical mechanical polishing process a surface of an item, such as a wafer, is made planar (e.g., substantially flat) by holding the wafer (e.g., using a rotating carrier) against a rotating polishing table that contains an abrasive slurry. Material is removed to render the exposed surface planar. The rate that the material is removed from the wafer depends upon the pressure applied between the carrier and the polishing table pads, temperature, polishing time and type of slurry utilized. If too much material is removed the item being polished may have to be scrapped. If too little material is removed, the item will not be properly planarized and must be reworked/repolished.
Conventional CMP control strategies and practices require extensive xe2x80x9csend aheadxe2x80x9d measurements to remove the right amount of material. In other words, conventional systems determine the correct polishing time, pressure and slurry makeup by performing experiments on various test batches of wafers. Once the correct recipe of time, pressure and slurry is determined, it is applied to production wafers. Also, xe2x80x9csend aheadxe2x80x9d production wafers are periodically sampled after being polished to evaluate the polishing process. The polishing process is then adjusted accordingly. For example, if the wafers are under-polished the polishing time, pressure or temperature may be increased. If the wafers are overpolished, they may be scrapped and the polishing time, pressure and temperature may be decreased.
However, such conventional systems often destroy large numbers of wafers because an under-polishing or over-polishing situation cannot be detected until after it has occurred (e.g., silent failures), at which point many defective wafers which were made before the silent failure was detected may have to be scrapped or reworked. Therefore, there is a need for a polishing system which measures the polishing rate in real-time and eliminates or reduces the amount of scrap associated with xe2x80x9csend aheadxe2x80x9d measurement techniques.
It is, therefore, an object of the present invention to provide a structure and method for polishing a device that includes oscillating a carrier over an abrasive surface (the carrier bringing a polished surface of the device into contact with the abrasive surface, the oscillating allowing a portion of the polished surface to periodically oscillate off the abrasive surface), optically determining a reflective measure of a plurality of locations of the polished surface as the portion of the device oscillates off the abrasive surface and calculating depths of the locations of the polished surface based of the reflective measurement.
The invention may also include calculating a rate of material removal based on the depths of the locations of the polished surface, calculating a change of material composition of the polished surface based on a change in the reflective quality, and/or calculating a thickness of a layer of the polished surface based on the depths of the locations of the polished surface.
The invention also includes rinsing the polished surface as the carrier oscillates off the abrasive surface. The calculating of the depths preferably determines a smallest of the depths. The invention may also remove a pattern of the light source from the reflective measure to accommodate for background characteristics.
Therefore, the invention provides a system and method for measuring the thickness of a material being polished in real time using optical measuring techniques. The invention includes a water jacket which removes any abrasive material and increases the accuracy of the optical measurement. Further, the invention avoids the problem of spectral smearing by utilizing a high-speed strobe during the optical analysis of the surface be polished.
In addition, the invention measures the thickness of many points on the surface being polished to increase the thickness measurement accuracy. Further, the invention provides a very accurate endpoint detection system (for transparent and non-transparent materials) by observing the optical index change.
Therefore, the invention overcomes the production loss and excessive scrap associated with conventional send ahead measurement techniques.